1. Reset Internet Explorer settings by opening the program, clicking the 'Tools' menu and clicking 'Internet Options.' Click the 'Advanced' tab and then click 'Reset' in the 'Reset Internet Explorer Settings' window to confirm.
2. Download and install the latest version of Internet Explorer from the Microsoft website. If you're running an outdated version of the browser, upgrading may solve the the MSHTML.DLL error by replacing the file. When finished installing, restart your computer, then open the browser and navigate to an HTML page to test.
3. Install the latest service pack upgrade for your version of the Windows operating system. Go to the Microsoft Update website and choose 'Express Install.' Choose to install the latest updates for your computer, then restart.
4. Run the System File Checker program. This built-in utility checks important system files and automatically replaces missing or corrupted files. Click the 'Start' menu, then choose 'Run.' In the text area, type 'sfc /scannow' and press the 'Enter' key. If any files are found to be missing or corrupted, you'll need to insert your Windows disc into your optical drive so the files can be replaced. Restart your computer once the program has completed the check.
5. Reset the TCP/IP protocol settings on your computer. Click the 'Start' menu and choose 'Run.' Type in 'cmd' to open the command prompt window. Type in 'netsh int ip reset resetlog.txt' and press the 'Enter' key. This will rewrite two registry entries that are used by the TCP/IP Internet protocol, which may solve the DLL error. Restart the computer.
6. Download and install a registry cleaner that checks the Windows registry for errors and fixes or deletes corrupted entries. Run the registry cleaner to check for errors, opting to fix any that are detected, and then restart the computer.
7. Test the result of any or all of these steps by opening Internet Explorer and browsing to any Web page with the file extension '.htm' or '.html'. If the program renders the pages without error, the MSHTML.DLL file has been successfully fixed or replaced.